Process for producing fiber of ultra high molecular weight
polyethylene

ABSTRACT

A process for producing fiber of ultra high molecular weight polyethylene, with a flat cross-section and high cohesiveness, is disclosed. The process includes: distributing the powder of UHMWPE into a solvent evenly; preparing an uniform emulsion mixture by properly untangling with high shear; at the same time adding polar polymer comprising polar groups, for example a carboxyl group, a carbonyl group, an ether group, or an ester group and so on; evenly distributing the polar polymer together with the polyethylene powder in the solvent to form an uniform emulsion mixture; forming a gel filament from the emulsion mixture by gel spinning method, then extracting, drying, and stretching so as to obtain the UHMWPE fiber, with a flat cross section, high strength and cohesiveness. By properly untangling, the swelling and dissolving of the ultra high molecular weight polyethylene can be accelerated, while the polar polymer being evenly distributed therein can significantly improve the adhesive property of the fiber. The operations in the production method are easy, and furthermore, time, labor and cost can be saved. The section of the fiber is of a flat rectangle shape and the wall is thin and even, so the path for the solvent in the fiber diffusing out of the gel filament can be significantly shorten, and thus the efficiency of extraction and the uniformity of the fiber can be improved.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national stage application under 35 U.S.C. §371 of International Patent Application No. PCT/CN2007/002906, designating the United States and filed on Oct. 9, 2007, which claims the benefit of priority under 35 U.S.C. §119(a) to Chinese Patent Application Nos. 200610118076.X, filed Nov. 8, 2006, 200610147424.6, filed Dec. 18, 2006, 200710040678.2, filed May 15, 2007, and 200710043831.7, filed Jul. 16, 2007, all of which are hereby incorporated by reference in their entirety.

FIELD OF THE INVENTION

The invention relates to a method of preparing fiber of High Molecular Weight Polyethylene (HMWPE), specifically, a method of preparing fiber of Ultra High Molecular Weight Polyethylene (UHMWPE).

BACKGROUND OF THE INVENTION

A method of preparing a high strength, high modulus polyethylene (PE) fiber from UHMWPE gel via drawing or stretching technology is disclosed in UK Patent Nos. GB2042414 and GB2051667, assigned to DSM Company, Netherlands in 1979. After that, this technology was industrialized by Allied Company from the U.S., Toyobo-DSM Company, a joint venture by Japan and Netherlands, as well as Mitsui Company from Japan. In 1982, Allied Company obtained U.S. Pat. No. 4,413,110, which covers a process of preparing UHMWPE fiber. Donghua University in China also obtained Chinese Patent Nos. 89107905 and 97106768 in this area.

The main procedures for preparing UHMWPE gel fiber are as follows: UHMWPE is added into a suitable solvent to prepare a solution by stirring; the solution is extruded by an extruder and spun through a spinnerette, followed by cooling, extraction, drying, and stretching, to form the desired fiber product. To obtain a high strength and high modulus fiber, key steps include the preparation of a homogeneous UHMWPE solution, and the extraction with a second solvent to remove the large amount of a first solvent contained in gel fiber prior to stretching of the gel fiber.

As the molecular weight of polyethylene increases, its macromolecular size is also increasing, and the entanglement exists among such macromolecules. The entanglement among the macromolecules is beneficial to increase the draw ratio and can result in highly oriented fiber with higher strength and modulus. However, the viscoelastic effect due to the entanglement among the macromolecules of polymer makes the dissolving process much more complicated, and is not beneficial to the dissolving and shaping process. Therefore, the entanglement among the macromolecules should be controlled. The state of such entanglement can be controlled by heat treatment, solvent treatment and cutting.

The molecular weight for polymer and low molecule solvent is quite different. Polymer has a long molecule chain and it is difficult for the polymer to move. Due to the strong intra-molecular interactions and entanglement among the polymer molecules, the polymer does not diffuse into a solvent when the polymer and low molecule solvent are just mixed. If the conventional dissolution method is used to prepare the solution, the polymer powder tends to be aggregated, or form a gel solid due to incomplete permeation of the solvent, and a homogeneous solution cannot be obtained. Furthermore, the Weissenberg Effect (climbing effect) will appear due to the viscoelastic effect caused by entanglement between macromolecules of polyethylene when stirring.

With the increase of molecule weight, polymer concentration and stirring speed, the Weissenberg Effect will be more effective. Accordingly, it will become more difficult to obtain a homogeneous solution.

Certain patents propose various methods for solving the problem. For example, EP 0255618 discloses that a hydrocarbon mixture free of naphthalin and diphenyl, with boiling point around 180-250° C. is obtained after a rectification separation from hydrogenated coal oil. Such hydrocarbon mixture is further mixed with UHMWPE and decahydronaphthalene at 135° C., agitated for several hours to form a PE solution. The concentration of the PE solution is no greater than 50%.

Japanese Patent No. 59232123 describes a process to mix UHMWPE with small amount of a solvent for several minutes, followed by heating, then more solvent is added gradually with stirring to form a solution containing UHMWPE.

In an example disclosed in Japanese Patent No. 63-15838, a fractional coal oil is catalytically hydrogenated to provide a solvent. The solvent is further added with an anti-oxidant and PE, and the resulting mixture is agitated for 3 hours at 140° C. to form a 10% (w/w) UHMWPE solution.

In some cases, the problem is solved using a two-step process including swelling and dissolving. Chinese Patent No. 970106768 discloses that an alkane hydrocarbon solvent can be used to swell PE under certain conditions, and to prepare a suspension solution containing UHMWPE.

Chinese Patent No. 97101010 describes that a pre-swelling pan equipped with an new mixer baffle is used to swell UHMWPE to form a suspension solution so as to avoid the Weissenberg Effect of UHMWPE during dissolving and stirring.

Chinese Patent No. 20041009607615, titled “A Method For Continuous Mixing and Preparation of UHMWPE Solution,” discloses the use of a static mixer with a screw having a small Length/Diameter ratio to allow continuous preparation of UHMWPE solution. In Chinese Patent No. 85107352A, DSM company provides a method of preparing a homogeneous solution of polymer, comprising: feeding a fine polymer powder and a solvent into an extruder, where a suspension and a solution is formed within the extruder, with an operation temperature above the melting point of the polymer and at a mechanical cutting rate of about 30-2000 S⁻¹. However, this method can damage the molecule chain of UHMWPE and result in a decrease of its molecular weight.

Although the patents mentioned above made certain improvements on the process related to solvent and dissolving, the following problems still exist: the processing equipment is complicated; the process is not stable. In addition, there is a safety risk associated with the process, and the tenacity of so obtained fiber is decreased.

The fiber with high strength and high modulus can be obtained only after large amount of the first solvent contained in the gel fiber is extracted with a second solvent and the stretching of the gel fiber is performed. The extraction speed depends on the second solvent used, the extraction process, as well as the diffusion path of the solvent. During the course of the extraction, the solvent in the outer surface of the fiber will first diffuse from the gel fiber. The longer the diffusion distance, the bigger the difference in diffusion speeds. According to the current method, the cross section of a PE gel fiber is round and has a thicker wall. The bigger the difference, the easier to form a skin-core structure, which is not a homogeneous structure and which has a negative influence on the stretching process so as to affect the mechanical properties of the fiber product.

Currently, there are some patents related to the preparing of profiled HDPE fiber membrane, including U.S. Pat. Nos. 4,115,492, 5,294,338, 6,436,319 and ZL200510049263, all of which use melting spinning; and U.S. Pat. No. 5,695,702 and ZL95193838, which use thermoplastic hollow fiber membrane module and method of manufacture. The methods described therein above suffer the problem of high cost, while the homogeneity of the fiber structure obtained is not satisfying.

Furthermore, the preparation of high strength and high modulus PE fiber by stretching or drawing UHMWPE gel fiber has already been industrialized. The searched patents for PE gel fiber include EP 0205960A, EP 0213208A1, U.S. Pat. No. 4,413,110, WO 01/73173A1, and EP 1746187A1, which made some modifications on spinning technology. For the UHMWPE gel spinning process, it is critical to obtain a homogeneous polymer solution and a stable drawing of gel fiber. As a pre-condition for the formation of fiber with stable properties, it is important to have a good solution and a stable drawing operation.

Because PE fiber has the advantages of light weight, flexible, high strength and high modulus, UV-proof, anti-impact, and anti-corrosion to seawater, it can be used for cutting-proof gloves, bullet-proof jacket or helmet, cable etc. In most circumstances, one kind or several kinds of base materials, such as acrylonitrile butadiene rubber, polyurethane and epoxy resin, can be combined with the PE fiber. Due to the inertia surface of the PE fiber, the interface adhesion between the fiber and the base material is poor, which has brought great attention of those skilled in this field. To improve the interface adhesion strength between the fiber and the base resin, certain methods of surface treatment, including surface grafting improving, chemical agent etching, plasma processing, corona arc treatment, and photo-oxidation surface modification, etc., have been used to activate the inertia surface of the PE fiber.

U.S. Pat. No. 480,136 discloses that during spinning, thermal initiated surface silanization grafting reaction occurs on PE fiber, with a further cross-linking process, and results in the improvement of the adhesive property of the PE fiber. However, the process has a negative influence on the subsequent drawing process, and the mechanical properties of the fiber is not satisfying. U.S. Pat. No. 5,039,549, U.S. Pat. No. 5,755,913 and ZL03115300.3 describe that plasma, ozone, corona arc or UV radiation can be used to improve the adhesive property on PE fiber surface. However, these processes are complicated and involve expensive equipment, and the process parameters are difficult to control. Therefore, the processes are difficult to be industrialized.

Jiang Shen et al. proposes to use strong oxidizing agents, such as chromic acid, kali permanganate, to etch the surface of the PE fiber (see, UHMWPE Fiber Adhesive Property Study, Reinforced Glass/Complex Material, 2004(3):47). Because this method requires the merging of the PE fiber in a strong oxidation environment for a long time, while the fiber infiltrating property may be improved, the mechanical properties of the fiber is decreased. In addition, such processes are also complicated, with a strict requirement on the equipment, and also have the pollution problem from the waste liquid.

CN163544 proposes to use a composite extracting agent containing polar polymer compound to treat the spinned PE gel fiber to improve the adhesive property on the fiber surface while maximally maintaining the original strength of the fiber. This process is relatively simple, without requiring any additional equipment. Although this process is efficient for loose gel fiber, in practical production with tension extraction, it is difficult for polar polymer compound to diffuse into gel fiber, and therefore, the improvement made on the adhesive property is not apparent.

DESCRIPTION OF THE INVENTION

The present invention is to solve the existing technical problems in UHMWPE fiber production, and specifically to solve the problem in the preparation of homogeneous solution containing raw material, and in the removal of the first solvent from the gel fiber. One objective of the present invention is to provide a simple, efficient and low cost method to prepare the HMWPE fiber. The HMWPE fiber prepared by this method has high adhesive property.

In particular, the technical problems can be solved by the following methods.

The method of preparing UHMWPE fiber comprises: mixing PE powder having a relative average molecule weight (MW) of 1 million to 6 million with polar polymer in a solvent, to form an emulsion mixture; the mixture being fed into an extruder with agitation, where the mixture swells and dissolves rapidly to form a transparent and homogeneous solution; and the solution being extruded through an spinnerette to spin into a gel filament, followed by cooling, extraction, drying and stretching (or drawing) to produce the desired UHMWPE fiber.

During the preparation of the emulsion mixture according to the present invention, the PE powder having a relative MW of 1 million to 6 million is mixed with polar polymer and solvent in an appropriate ratio, and the resulting mixture is fed into an untwisting equipment to untwist, and thereby forming a uniform emulsion mixture.

The concentration of the above-mentioned uniform emulsion mixture is about 4% to 60% (wt).

The polar polymer mentioned above includes polar polymer containing ester group, carbonyl group or ether group. The polar polymer containing ester group, carbonyl group or ether group refers to ethylene/vinyl acetate co-polymer, polyacrylates, polyethylene pyrrolidone/vinyl acetate co-polymer with different K value, polyoxyethylene polymer, or mixtures thereof.

The added weight % for the polar polymer relative to the UHMWPE powder with relative MW of 1 million to 6 million is about 1-10%, preferably about 2-8%.

In the untwisting process mentioned above, silicone oil or its derivative can be used for untwisting. Additionally, silicone oil or its derivative can also be used during the cooling (solidifying) process. Silicone oil or its derivative may comprise about 0.05-5 wt % of the UHMWPE fiber.

During the untwisting process mentioned above, one or more antioxidant, stabilizer, coloring agent, fire retardant can be added.

In the process mentioned above, the untwisting equipment may provide a cutting speed of at least 1000 S⁻¹, preferably 1000-5000 S⁻¹, and more preferably 2000-4000 S⁻¹. The untwisting equipment mentioned above can be high-speed dispersion machine, agitator (intensive mixing vessel), colloid mill, homogenizer, venturi, or any combinations thereof.

In the method mentioned above, the preferred relative average MW for UHMWPE is 4 million to 6 million, and more preferably 2 million to 5 million.

In the process to prepare the uniform emulsion mixture according to the present invention, the solvent used is liquid under room temperature, and it may be alkane (or paraffin) or its derivative, cycloalkane (or cycloparaffin) or its derivative, aromatic hydrocarbon or its derivative, or mixtures thereof.

In the process to prepare the homogeneous solution according to the present invention, the nominal concentration for the UHMWPE and the solvent is 1-50 wt %.

The extruder used in the present invention includes single screw, double-screw, triple-screw or four-screw extruder, where the extruding temperature is above the melting point of the UHMWPE, for example, 80-250° C. as the working temperature for the extruder.

The double-screw extruder can rotate in same direction or reverse direction, and the screw's length/diameter ratio is 1:30-65.

In one embodiment of the present invention, the uniform emulsion mixture stays in the double-screw extruder for 10-60 minutes (residence time), and preferably 20-40 minutes; with a material temperature inside the extruder at 50-280° C., and the extruding temperature for gel spinning at 140-280° C., preferably at 200-260° C.

In another embodiment, the spinnerette of the extruder has a rectangle shape, with a Length/Width ratio of 4-20, preferably 5-15.

In another embodiment, the emulsion mixture can be fed into the extruder directly, or via a storage vessel with an agitator (e.g., mixing vessel). The vessel can be one set or more than two sets.

In the drawing (or stretching) process of this invention, the drawing temperature for fiber is 80-130° C., at a draw ratio of more than 20/1, preferably 30/1-60/1.

Compared with existing technologies, the present invention has the following advantages:

-   -   1 UHMWPE fiber with PU or butyronitrile glove, is flexible and         light, and has anti-corrosive, anti-aging, and anti-oil         properties, and is the best option for the preparation of         cutting-proof glove on the market. However, due to the inertia         of PE, the adhesive interaction between PE and PU or PE and         butyronitrile is poor. The present invention utilizes a cutting         untwisting process to prepare UHMWPE. In addition, polar polymer         containing ester group, carbonyl group and/or ether group is         added to the UHMWPE. As a result, the polar polymer is evenly         distributed in the UHMWPE so as to provide a PE fiber with high         adhesive property. This process is simple and does not need any         additional equipment.     -   2 The emulsion mixture containing UHMWPE and a suitable amount         of polar polymer undergo high speed cutting, swelling as well as         complete dissolving in a double screw extruder. This is helpful         to minimize the degradation of the polymer, and thereby         improving the adhesive property without affecting the mechanical         property of the fiber.     -   3 In addition to the use of high speed cutting to untwist         UHMWPE, a suitable amount of carbon chain polar polymer         containing polar side groups such as ester group, carbonyl group         or carboxy group can be added to improve the adhesive property         of the PE without affecting its rupture strength (tenacity).     -   4 The UHMWPE fiber prepared by the method of the present         invention has high rupture strength (tenacity) and strong energy         absorption, and provides maximum rupture extension (elongation)         while maintaining enough rupture strength, which allows to         achieve an optimized balance between rupture strength and         rupture extension. This material is suitable for the preparation         of cutting-proof glove. This invention uses rapid swelling and         dissolving of UHMWPE by a high speed cutting and untwisting         process to ensure that the rupture strength for the fiber is         above 30 CN/dtex with a rupture level of more than 30030         CN/dtex.     -   5 Usually, the fiber used in the cutting-proof glove has a         single layer. In addition to good cutting-proof performance, the         glove is also required to be even and homogeneous in density.         This, it imposes a higher demand on fiber homogeneity.         Currently, the CV value for titer and strength of UHMWPE fiber         is about 8-10%. The present invention can achieve a CV value for         titer and strength of the UHMWPE fiber at about 4-6%, by         utilizing rapid swelling and dissolving of UHMWPE and addition         of a surface active agent in a cooling (solidifying) solution,         as well as the design of a flat filament structure.     -   6 In accordance with the present invention, the UHMWPE fiber has         a flat structure. As a result, the specific surface area of the         fiber is increased, which is beneficial for solidifying evenly         and shortening the distance for the diffusion of the solvent         from the gel fiber. Accordingly, this method can increase the         extraction rate, reduce the amount of the second solvent used in         extraction and lower the cost, and also improve the homogeneity         and strength of the fiber.     -   7 Utilizing suitable untwisting, the method of the present         invention not only makes the process simple, saves cost,         manpower and time, but also makes dissolving more homogeneous.

Specific Embodiments

To facilitate the understanding of the technical approach, innovation characteristics, and final results and functions of the present invention, the following examples are provided to further illustrate the invention.

Example 1

UHMWPE (Relative Average Molecule Weight 4.5M) powder and #90 solvent white oil with a weight ratio of 1:8, were fed into an untwisting pan at room temperature, and underwent cutting for 10 minutes at a speed of 2000 S⁻¹ under N₂ protection, to form a homogeneous emulsion mixture. The mixture was fed into a same directional double screw extruder (intake diameter=Φ25 mm, Length/Diameter ratio=36, temperature=250° C., the screw rotation speed=35 rpm). The extruded material was filtered, and spun into a gel filament through a spinnerette, then extracted and stretched at a stretch ratio of 35, to provide UHMWPE.

Example 2

UHMWPE (Relative Average Molecule Weight 4.5M) powder and #90 solvent white oil with a weight ration of 1:8 were fed into an untwisting pan at room temperature, and further added EVA28190 (ethylne-vinyl acetate co-polymer, with vinyl acetate comprising 28%, melting index=190) with an amount of 4% by weight of the UHMWPE powder, and underwent cutting for 10 minutes under N₂ protection at a speed of 2000 S⁻¹, to form a homogeneous emulsion mixture. The mixture was fed into a same directional double screw extruder (intake diameter =Φ025 mm, Length/Diameter ratio=36, temperature=250° C., the screw rotation speed=35 rpm). The extruded material was filtered, and spun into a gel filament through a spinnerette, then extracted and stretched at a draw ratio of 35, to produce UHMWPE with high adhesive properties.

Example 3

UHMWPE (Relative Average Molecule Weight 4.5M) powder and #90 solvent white oil with weight ratio of 1:8 were fed into an untwisting pan at room temperature, and further added EVA28190 (ethylene-vinyl acetate co-polymer, with vinyl acetate comprising 28%, melting index=190) with an amount of 2% by weight of the UHMWPE powder, and underwent cutting for 10 minutes under N₂ protection at a speed of 2000 S⁻¹, to produce a homogeneous emulsion mixture. The mixture was fed into a same directional double screw extruder (intake diameter=Φ25 mm, Length/Diameter ratio=36, temperature=250° C., the screw rotation speed=35 rpm). The extruded material was filtered, and spun into a gel filament through a spinnerette, then extracted and stretched at a draw ratio of 35, to produce UHMWPE with high adhesive properties.

Example 4

UHMWPE (Relative Average Molecule Weight 4.5M) powder, is mixed with #90 solvent white oil with weight ratio of 1:8 were fed into an untwisting pan at room temperature, and further added EVA1030 (ethylene-vinyl acetate co-polymer, with vinyl acetate comprising 10%, melting index=30) with an amount of 4% by weight of the UHMWPE powder, and underwent cutting for 10 minutes under N₂ protection at a speed of 2000 S⁻¹, to produce a homogeneous emulsion mixture. The mixture was fed into a same directional double screw extruder (intake diameter=Φ25 mm, Length/Diameter ratio=36, temperature=250° C., the screw rotation speed=35 rpm). The extruded material was filtered, and spun into a gel filament through a spinnerette, then extracted and stretched at a draw ratio of 35, to produce UHMWPE with high adhesive properties.

Example 5

UHMWPE (Relative Average Molecule Weight 4.5M) powder and #90 solvent white oil with weight ratio of 1:8 were fed into an untwisting pan at room temperature, and further added polyacrylate with an amount of 2% by weight of the UHMWPE powder, and underwent cutting for 10 minutes under N₂ protection at a speed of 2000 S⁻¹, to produce a homogeneous emulsion mixture. The mixture was fed into a same directional double screw extruder (intake diameter=Φ25 mm, Length/Diameter ratio=36, temperature=250° C., the screw rotation speed=35 rpm). The extruded material was filtered, and spun into a gel filament through a spinnerette, then extracted and stretched at a draw ratio of 35, to produce UHMWPE with high adhesive properties.

Example 6

UHMWPE (Relative Average Molecule Weight 4.5M) powder and #90 solvent white oil with weight ratio of 1:8 were fed into an untwisting pan at room temperature, and further added polyoxyethylene with an amount of 4% by weight of the UHMWPE powder, and underwent cutting for 10 minutes under N₂ protection at a speed of 2000 S⁻¹, to form a homogeneous emulsion mixture. The mixture was fed into a same directional double screw extruder (intake diameter=Φ25 mm, Length/Diameter ratio=36, temperature=250° C., the screw rotation speed=35 rpm). The extruded material was filtered, and spun into a gel filament through a spinnerette, then extracted and stretched at a draw ratio of 35, to produce UHMWPE with high adhesive properties.

The mechanical and adhesive properties of the UHMWPE fiber prepared according to Example 1 (without the addition of polar polymer) and Example 2-6 are listed in Table 1.

TABLE 1 Mechanical Properties and Adhesive Strength of UHMWPE Fiber Prepared According to This Invention Rupture Rupture Strength Young's Extension Pull-out (Tenacity) Modulus (Elongation) Strength Example No. CN/dtex CN/dtex CN/dtex CN/dtex 1 35.25 972 4.07 10.23 2 31.31 939 4.42 26.73 3 33.63 953 4.26 20.54 4 31.09 926 4.19 21.59 5 30.95 896 4.91 29.06 6 33.73 977 4.15 18.77

The following procedure is used to measure the adhesive strength of the UHMWPE fiber: The UHMWPE fiber is passed through a capsule with small hole, the height of the capsule being about 7 mm. An epoxy resin and a solidifying agent are mixed at a ratio of 4:1, and charged into the capsule, and allow for solidifying for 48 hours. The embedded length L(mm) of the fiber in the capsule is measured, using a pull-out experiment, which utilizes DXLL-20000 Strong Power Device to measure the adhesive properties between the UHMWPE fiber and epoxy resin (clamping distance=200 mm; dropping speed=50 mm/min.; and the pull-out strength of the fiber can be calculated by the following formula: Pull-out strength=tested strength*7/L.

Example 7

UHMWPE (Relative Average Molecule Weight 4.5M) powder and #90 solvent white oil with a nominal concentration of 10% (wt) were fed into an untwisting pan at room temperature, and underwent cutting for 5 minutes under N₂ protection at a speed of 3000 S⁻¹, to form a homogeneous emulsion mixture. The mixture, with agitation, was fed into a same directional double screw extruder via a storage vessel (extruder diameter=Φ25 mm, Length/Diameter ratio=45, temperature=250° C., the screw rotation speed=35 rpm). The extruded material passed through a filter tank and a metering pump to get a measurement, and spun into a gel filament through a spinnerette, passed through a water bath, followed by extraction, drying and stretching at a draw ratio of 40, to produce UHMWPE fiber with Rupture Strength (i.e., Tenacity) of 30 cN/dtex and Young's Modulus of over 1000 cN/dtex.

Example 8

UHMWPE (Relative Average Molecule Weight 5 M) powder and #90 solvent white oil with a nominal concentration of 5% (wt) were fed into an untwisting pan at room temperature, and underwent cutting for 5 minutes under N₂ protection at a speed of 3000 S⁻¹, to form a homogeneous emulsion mixture. The mixture, with agitation, was fed into a double screw extruder via a storage vessel (extruder diameter=Φ25 mm, Length/Diameter ratio=64, temperature=250° C., screw rotation speed=50 rpm). The extruded material was passed through a filter tank and a metering pump to get a measurement, and spun into a gel filament through a spinnerette, passed through a water bath, followed by extraction, drying and stretching at a draw ratio of 40, to produce UHMWPE fiber with Rupture Strength of 28 cN/dtex and Young's Modulus of over 900 cN/dtex.

Example 9

UHMWPE (Relative Average Molecule Weight 4.5 M) powder and #90 solvent white oil with a nominal concentration of 5% (wt) were fed into an untwisting pan at room temperature, and further added 0.2% (wt) of an anti-oxidant, and underwent cutting for 5 minutes under N₂ protection at a speed of 2000 S⁻¹, to form a homogeneous emulsion mixture. The mixture, with agitation, was fed into a double screw extruder via a storage vessel (extruder diameter=Φ25 mm, Length/Diameter ratio=24, temperature=240° C., screw rotation speed=50 rpm). The extruded material was passed through a filter tank and a metering pump to get a measurement, and spun into a gel filament through a spinnerette, passed through a water bath, followed by extraction, drying and stretching at a draw ratio of 40, to produce UHMWPE fiber with Rupture Strength of 28 cN/dtex and Young's Modulus of over 900 cN/dtex.

Example 10

UHMWPE (Relative Average Molecule Weight 5 M) powder and #90 solvent white oil with a nominal concentration of 12% (wt) were fed into an untwisting pan at room temperature, and underwent cutting for 10 minutes under N₂ protection at a speed of 2000 S⁻¹, to form a homogeneous emulsion mixture. The mixture, with agitation, was fed into a double screw extruder via a storage vessel (extruder diameter=Φ25 mm, Length/Diameter ratio=24, temperature=250° C., screw rotation speed=30 rpm). The extruded material was passed through a filter tank and a metering pump to get a measurement, and spun into a gel filament through a spinnerette, passed through a water bath, followed by extraction, drying and stretching at a draw ratio of 40, to produce UHMWPE fiber with Rupture Strength of 35cN/dtex and Young's Modulus of over 1050 cN/dtex.

Example 11

UHMWPE (Relative Average Molecule Weight 4.5 M) powder and #90 solvent white oil with a nominal concentration of 10% (wt) were fed into an untwisting pan at room temperature via a spiral propeller at a speed of 0.5 kg/min, and underwent cutting under N₂ protection at a speed of 1000 S⁻¹, to form a homogeneous emulsion mixture. The mixture, with agitation, was fed into a double screw extruder via a storage vessel (extruder diameter=Φ25 mm, Length/Diameter ratio=24, temperature=250° C., screw rotation speed=30 rpm). The extruded material was passed through a filter tank and a metering pump to get a measurement, and spun into a gel filament through a spinnerette, passed through a water bath containing 2% polyether-epoxy modified silicone oil, followed by extraction, drying and stretching at a draw ratio of 40, to produce UHMWPE fiber with Rupture Strength of 30 cN/dtex and Young's Modulus of over 1000 cN/dtex.

Example 12

UHMWPE (Relative Average Molecule Weight 4.5 M) powder and #70 solvent white oil with a nominal concentration of 12% (wt) were fed into an untwisting pan at room temperature, and underwent cutting for 15 minutes under N₂ protection at a speed of 1000 S⁻¹, to form a homogeneous emulsion mixture. The mixture, with agitation, was fed into a double screw extruder via a storage vessel (extruder diameter=Φ25 mm, Length/Diameter ratio=24, temperature=250° C., screw rotation speed=30 rpm). The extruded material was passed through a filter tank and a metering pump to get a measurement, and spun into a gel filament through a spinnerette, passed through a water bath, followed by extraction, drying and stretching at a draw ratio of 40, to produce UHMWPE fiber with Rupture Strength of 30 cN/dtex and Young's Modulus of over 1000 cN/dtex.

Example 13

UHMWPE (Relative Average Molecule Weight 4.5 M) powder and #70 solvent white oil with a nominal concentration of 10% (wt) were fed into an untwisting pan at room temperature, and further added 1% (wt) of epoxy modified silicone oil, and underwent cutting for 5 minutes under N₂ protection at a speed of 3000 S⁻¹, to form a homogeneous emulsion mixture. The mixture, with agitation, was fed into a double screw extruder via a storage vessel (extruder diameter=Φ25 mm, Length/Diameter ratio=24, temperature=250° C., screw rotation speed=50 rpm). The extruded material was passed through a filter tank and a metering pump to get a measurement, and spun into a gel filament through a spinnerette, passed through a water bath, followed by extraction, drying and stretching at a draw ratio of 40, to produce UHMWPE fiber with Rupture Strength of 30 cN/dtex and Young's Modulus of over 1000 cN/dtex.

Example 14

UHMWPE (Relative Average Molecule Weight 5 M) powder and #90 solvent white oil with a nominal concentration of 12% (wt) were fed into an untwisting pan at room temperature, and underwent cutting for 10 minutes under N₂ protection at a speed of 2000 S⁻¹, to form a homogeneous emulsion mixture. The mixture, with agitation, was fed into a double screw extruder via a storage vessel (extruder diameter=Φ25 mm, Length/Diameter ratio=24, temperature=250° C., screw rotation speed=30 rpm). The extruded material was passed through a filter tank and a metering pump to get a measurement, and spun into a gel filament through a spinnerette, passed through a water bath containing 1.5wt % of epoxy modified silicone oil, followed by extraction, drying and stretching at a draw ratio of 40, to produce UHMWPE fiber with Rupture Strength of 35 cN/dtex and Young's Modulus of over 1050 cN/dtex.

Example 15

UHMWPE (Relative Average Molecule Weight 4.5 M) powder and #90 solvent white oil with a nominal concentration of 10% (wt) were fed into an untwisting pan at room temperature via a spiral propeller at a speed of 0.5 kg/min, and underwent cutting under N₂ protection at a speed of 1000 S⁻¹, to form a homogeneous emulsion mixture. The mixture, with agitation, was fed into a double screw extruder via a storage vessel (extruder diameter=Φ25 mm, Length/Diameter ratio=24, temperature=250° C., screw rotation speed=30 rpm). The extruded material was passed through a filter tank and a metering pump to get a measurement, and spun into a gel filament through a spinnerette, passed through a water bath containing 2% polyether-epoxy modified silicone oil, followed by extraction, drying and stretching at a draw ratio of 30, to produce UHMWPE fiber with Rupture Strength of 30 cN/dtex and Young's Modulus of over 1000 cN/dtex,

Example 16

UHMWPE (Relative Average Molecule Weight 4.5 M) powder and solvent white oil were mixed to prepare a homogeneous solution with a concentration of 8% (wt) and fed into a double screw extruder (extruder diameter=025 mm, Length/Diameter ratio=24, temperature=240° C., screw rotation speed=30 rpm). The extruded material was passed through a filter tank and a metering pump to get a measurement, and spun into a gel filament through a spinnerette comprising apertures having a rectangular shape with a Length/Width ratio of 8, passed through a water bath, followed by extraction, drying and stretching at a draw ratio of 40, to produce UHMWPE fiber with Rupture Strength of 30 cN/dtex and Young's Modulus of over 1000 cN/dtex.

Example 17

UHMWPE (Relative Average Molecule Weight 4.5 M) powder and solvent white oil were mixed to prepare a homogeneous solution with a concentration of 10% (wt) and fed into a double screw extruder (extruder diameter=Φ25 mm, Length/Diameter ratio=24, temperature=250° C., screw rotation speed=40 rpm). The extruded material was passed through a filter tank and a metering pump to get a measurement, and spun into a gel filament through a spinnerette comprising apertures having a rectangular shape with a Length/Width ratio of 12, passed through a water bath, followed by extraction, drying and stretching at a draw ratio of 40, to produce UHMWPE fiber with Rupture Strength of 30 cN/dtex and Young's Modulus of over 1000 cN/dtex.

The above descriptions demonstrate the basic principles, main characteristics and advantages of the present invention. It should be understood by one of ordinary skill in the art that the present invention is not limited by the examples described hereinabove. The examples and descriptions described herein only illustrate the principles for this invention, and various changes and modifications may be made without departing from the spirit and scope of the present invention. Such changes and modifications are included in the scope of this invention. The claimed scope of the present invention is further illustrated by the appended claims and equivalents thereof. 

1-26. (canceled)
 27. A method for preparing UHMWPE fiber, comprising: mixing UHMWPE powder having a relative average molecular weight of 1 million to 6 million with polar polymer in a solvent to form an emulsion mixture; feeding the mixture into an extruder wherein the mixture swells and dissolves to form a solution; extruding the solution through a spinnerette to spin into a gel filament; and subjecting the filament to cooling, extraction, drying and stretching to provide the UHMWPE fiber.
 28. The method of claim 27, wherein the UHMWPE powder, the polar polymer and the solvent are fed into an untwisting equipment to untwist to form an emulsion mixture.
 29. The method of claim 27, wherein the concentration of the emulsion mixture is 4%-60%.
 30. The method of claim 27, wherein the polar polymer comprises an ester group, a carbonyl group or an ether group.
 31. The method of claim 27, wherein the polar polymer is selected from ethylene/vinyl acetate co-polymer, polyacrylates, polyethylene pyrrolidone/vinyl acetate co-polymer, polyoxyethylene polymer and mixtures thereof.
 32. The method of claim 27, wherein the amount of the polar polymer relative to the UHMWPE powder is 1-10% by weight.
 33. The method of claim 27, wherein the amount of the polar polymer relative to the UHMWPE powder is 2-8% by weight.
 34. The method of claim 28, wherein silicone oil or its derivative is added during said untwisting and/or cooling process, in which the silicone oil or its derivative comprises 0.05-5% by weight of the UHMWPE fiber.
 35. The method of claim 34, wherein at least one additional agent is added during the untwisting process, in which the additional agent is an antioxidant, a stabilizer, a coloring agent, a fire retardant or mixtures thereof.
 36. The method of claim 28, wherein the untwisting equipment provides a cutting speed of at least 1000 S⁻¹.
 37. The method of claim 28, wherein the untwisting equipment provides a cutting speed of 1000 to 5000 S⁻¹.
 38. The method of claim 28, wherein the untwisting equipment provides a cutting speed of 2000 to 4000 S⁻¹.
 39. The method of claim 28, wherein the untwisting equipment is selected from high-speed dispersion machine, mixer, colloid mill, homogenizer, venturi, and combinations thereof.
 40. The method of claim 27, wherein the UHMWPE has a relative average molecular weight of 4 million to 6 million.
 41. The method of claim 27, wherein the UHMWPE has a relative average molecular weight of 2 million to 5 million.
 42. The method of claim 27, wherein the solvent used to form an emulsion mixture is in liquid form at room temperature, and is selected from alkane or its derivative, cycloalkane or its derivative, aromatic hydrocarbon or its derivative, and mixtures thereof.
 43. The method of claim 27, wherein the nominal concentration of the UHMWPE powder in the solvent is 1-50wt %.
 44. The method of claim 27, wherein the extruder is selected from a single screw extruder, a double-screw extruder, a three-screw extruder, and a four-screw extruder, and wherein the operating temperature for the extruder is 80-250° C.
 45. The method of claim 44, wherein the double-screw extruder can rotate in same direction or reverse direction, and wherein the Length/Diameter ratio of the screw rod is 1:30-65.
 46. The method of claim 45, wherein the residence time for the emulsion mixture in the double-screw extruder is 10-60 minutes, material temperature inside the extruder is 50-280° C., and the temperature of the extruded gel filament is 140-280° C.
 47. The method of claim 46, wherein the residence time for the emulsion mixture in the double-screw extruder is 20-40 minutes, and the temperature of the extruded gel filament is 200-260° C.
 48. The method of claim 27, wherein the spinnerette comprises apertures having a rectangle shape with a Length/Width ratio of 4:20.
 49. The method of claim 27, wherein the spinnerette comprises apertures having a shape of rectangle with a Length/Width ratio of 5:15.
 50. The method of claim 27, wherein the emulsion mixture can be fed into the extruder directly or via a storage vessel equipped with an agitator.
 51. The method of claim 27, wherein the stretching is conducted at a temperature of 80-130° C. and at a draw ratio of at least 20/1.
 52. The method of claim 51, wherein the draw ratio from 30/1 to 60/1.
 53. UHMWPE fiber prepared according to the method of claim
 27. 